Double stream growing-wave amplifier



Aug. 18, 1959 J. A. RUETZ DOUBLE STREAM GROWINGMAVE AMPLIFIER 2 Sheets-Sheet 1 Filed Jan. 18, 1957 INVENTOR, JOHN A. RUETZ.

Aug. 18, 1959 J. A. RUETZ 2,900,559

DOUBLE STREAM GROWING-WAVE AMPLIFIER Filed Jan. 18, 1957 2 Sheets-Sheet 2 FIG. 4

INVENTOR, JOHN A; RUETZ Aff'arney States atent fiiice 2,990,559 Patented Aug. 18, 1959- DOUBLE STREAM GRGWING' WAVE AMPLIFIER John A. Ruetz, Mountain View, Calif., assignor to the United States of America as represented by the Secretary of the Army Application January 18, 1957, Serial No. 635,565

8 Claims. (Cl. 315-5.12)

The present invention relates to an improved electron discharge device for generating and amplifying energy in the high frequency ranges, and more particularly, to the producing of two or more intermixed beams of different velocities for use in double stream amplifiers of the traveling wave tube variety or the like.

In the prior art the two or more intermixed beams of different velocities, developed in a gun structure, were produced by the use of separate cathodes (either behind one another or closely side-by-side), one for each produced beam, so arranged that the beams would intermix.

The invention, as will be described herein, is an improvement in the prior art device in that a single cathode is used in the gun structure. This cathode emits a stream of electrons which is partly focused on an area of an electrode (dynode), the area having been coated with a good secondary electron emitting material. The part of the stream focused on the secondary emitting material causes emission of secondary electrons. The other part of the stream is allowed to pass unhampered through an aperture in the dynode. A second electrode (anode) at a higher DC. potential is used to accelerate and focus the secondary electrons and the unhampered primary ones. Thus, through utilizing the secondary emission effect two electron beams of different velocities are developed by the use of only one cathode.

An object of the invention is to provide a means of eliminating the complexity of a plural ibeam growingwave amplifier.

Another object of the invention is to provide a plural beam growing-wave amplifier comprising only one cathode.

A further object of the invention is to provide two electron beams of different velocities through the use of secondary emission. 1

Still another object of the invention is to utilize the two formed electron beams in a traveling wave tube or the like.

The exact nature of the invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawings in which:

Figure 1 is a longitudinal section view, partly schematic, of an electron tube according to the invention in which resonant cavities are utilized as control elements;

Figure 2 is a modification of Figure 1 wherein helices are substituted for the resonant cavities; and

Figs. 3, 4, 5, and 6 are pictorial views illustrating modifications of the aperture of the dynode shown in Figures 1 and 2.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Figure 1 (which illustrates a preferred embodiment) an electron discharge device for producing a beam of two intermixed groups of electrons, each having a different velocity. The device comprises gun structure 3, for initiating the two intermixed groups of electrons; drift region (interaction through the drift region 5; and second control element 9,

which in a known manner will extract energy from the waves of intermixed electrons; and collector electrode 11 operating at a potential suitable for intercepting all of the electrons which have passed through the drift region 5. These elements of the electron discharge device are housed in envelope 40.

The electron gun structure 3 comprises cathode 13 for emitting electrons; focusing electrode 15 for focusing the electrons into a stream; first electrode (dynode) 17 having an aperture 19 therethrough and substantially in the center thereof, a portion of the focused electronstream passing through the aperture 19 unhampered, and another portion of the focused electron beam striking the walls (coated with secondary emissive material) forming the aperture 19 so that secondary electrons will be emitted and also pass through the aperture 19; and second electrode (anode) 21 having an opening 23 therethrough for allowing the two beams to pass therethrough. The cathode 13, focusing electrode 15, dynode 17, and anode 21 are arranged substantially symmetrically about a common axis 25, not fully shown in the figures. The dynode 17 and anode 21 are also mounted substantially transversely to the electron beams. The particular electron gun structure herein described is particularly applicable to a traveling wave tube or the like.

The walls of aperture 19 are coated with a good secondary electron emitting material to enhance secondary emission, and are shaped to allow the secondary emitted electrons to form a beam and to move in the same direction as the unharnpered portion of the original electron stream that passes through the aperture 19 of dynode 17. The electrons striking the walls of aperture 19 of dynode 17 are multiplied and are accelerated and focused through the opening 23 in the anode 21.

The aperture 19 of dynode 17 can have a plurality of shapes as illustrated pictorially in Figures 3, 4, 5, and 6. In Figure 3, the aperture 19 is depicted as a slot, running transverse to the oncoming electron beam and having its walls beveled inwardly. Aperture 19 can also have a pyramidical frustum shape as depicted in Figure 4; a conical frustum shape as depicted in Figure 5; or wedge shape as depicted in Figure 6. In all of the figures, aperture 19 decreases in cross sectional area in the direction of the moving electron beams passing therethrough.

Referring again to Figure 1, a DC. source 27 is arranged so that the potentials of cathode 13, dynode 17, and anode 21 will be of an increasing order (cathode voltage V dynode voltage V and anode voltage V The first control element (input) 7 and second control element (output) 9 contained within the drift region 5 are of like structure, are substantially symmetrical with respect to axis 25, and are depicted, respectively, as cavities 7 and 9 in Figure 1. These two same control elements are depicted in Figure 2 as helices 7' and 9' and are substantially symmetrical about the axis 25'. Furthermore, each input control element 7 or 7 is provided with an input coaxial line 29, or 29 respectively for connecting an input signal thereto, and each output control element 9 or 9 is provided with an output coaxial line 31 or 31' respectively for removing a signal therefrom. The elements of the electron-discharge device of Figure 2 are enclosed in envelope 40.

Referring to Figure 1, the input resonant cavity 7 and the output resonant cavity 9 have associated therewith grids 33, 35 and 37, 39, respectively. These grids are substantially perpendicular to the path of the electrons, i.e., are transverse to the drift region. Although cavities 7 and 9 are shown with grids, it should be understood that the cavities may be replaced with cavities not having grids associated therewith.

From the description of the gun structure 3 so far disclosed, it is readily apparent that the electron beam formed by the electrons which passed through aperture 19 of dynode 17 without striking the walls thereof, 'i.e., unhampered electrons, will upon emerging from opening 23 of anode 27 have a velocity corresponding to a potential V The secondary electrons emitted from the walls of aperture 19 of dynode 17 and forming a second electron beam will have a variation in potential due to the velocity of secondary emission. However, this will be for most electrons of the order of 10 volts. Therefore,

the greater number of secondary electrons will have a lower velocity than the unhampered electrons and will correspond to a potential of (V V )+l volts.

When properly excited by a signal derived from coaxial line 29 the input cavity 7 will act in a known manner to velocity modulate the two beams of electrons which move between its grids 33, 35 thus forming two sets of electron waves. The interaction between the two sets of waves in the drift region (interaction region) causes one of the electron waves to grow in magnitude. The increase in the magnitude (wave energy) of the growing wave is attained at the cost of a lessening of an initial differential which is caused to exist between the kinetic energies of the two groups of electrons and by a phenomenon which has been described as a mechanism of elastic collisions between fast and slow electrons.

The output resonant cavity 9, in a well known manner, will extract energy from the waves of the intermixed electrons which pass between its grids 37, 39. This energy is transported by the output coaxial line 31 to a utilization circuit.

Beyond the output resonant cavity 9, in the direction of the electron travel, is collector electrode 11 which will operate at a potential suitable for intercepting all of the electrons which have passed through the drift region. These electrons may then be returned to the cathode 13 of theelectron gun 3.

The embodiment of Figure 2 is in all respects similar to that of Figure 1 with the exception that the input and output control elements consist of helices 7' and 9 respectively rather than resonant cavities. The helices 7 and 9 are connected in a conventional manner, i.e., each helix has one of its ends connected to an inner conductor of a coaxial line and the other connected to an outer conductor, the particular connection depending on whether the helix is used to velocity modulate the beams or extract energy therefrom.

In the preferred embodiment of the tube structure the emitted electrons are cause to follow paths substantially parallel to the axis 25 by means of a strong axial magnetic field produced by a source of magnetic flux which is not shown. electron beams together. However, the electrostatic optics should be able to focus sufliciently to allow onlythe interaction region (drift region) 5 to be in the magnetic field. A periodic magnetic field may also be utilized in place of the axial magnetic field for either the case of the magnetic field alone or in conjunction with the electrostatic optic case.

It should be understood, of course, that the foregoing disclosure relates to only preferred embodiments of the invention and that numerous modifications or alterations may be used therein without departing from the spirit and the scope of the invention as set forth in the appended claims.

What is claimed is:

. 1, An electron gun system for producing intermixed This axial magnetic field also holds the Cit 2,900,559 7 V V I r.

beams of electrons of different velocities, said gun system comprising a cathode for emitting primary electrons, a focusing electrode surrounding said cathode, a dynode having an aperture with tapering walls narrowing in the direction of travel of the electrons away from said cathode, said walls being coated with secondary emissive material so that primary electrons striking said walls produce secondary electrons, an anode beyond said dynode in the direction of travel of said electrons and having an aperture aligned with that of said dynode for accelerating said primary electrons and said secondary electrons away from said cathode, and means for maintaining said dynode at a higher positive potential than said cathode and said anode at a higher positive potential than said dynode.

2. The electron gun system of claim 1 wherein said aperture of said dynode is a slot running transverse to said intermixed beams of electrons, said slot having walls beveled inwardly. V

'3. The electron gun system of claim 1 wherein said aperture of said dynode has a pyramidical frustum shape and decreases in cross sectional area in the direction of said intermixed beams of electrons passing therethrough.

4. The electron gun system of claim 1 wherein said aperture of said dynode has a wedge shape and decreases in cross sectional area in the direction of said intermixed beams of electrons passing therethrough.

5. In an electron discharge device for producing intermixed beams of electrons of different velocities: an electron gun system having a cathode for emitting a stream of primary electrons, a focusing electrode surrounding said cathode, a dynode having an aperture with tapering walls narrowing in the direction of travel of said electrons away from said cathode, said Walls being coated with secondary emissive material, said stream of electrons being focused by said focusing electrode so that a first portion of said stream of electrons passes through said aperture and a second portion of said stream of electrons strikes said secondary emissive material causing secondary electrons to be emitted therefrom, an anode beyond said dynode in the direction of travel of said electrons and having an aperture aligned with that of said dynode for accelerating said primary electrons and said secondary electrons away from said cathode, thereby forming said intermixed beam of electrons of different velocities, means for maintaining said dynode at a higher positive potential than said cathode and said anode at a higher positive potential than said dynode, a drift region beyond said 7 anode in the direction of travel of said electrons having therein means for velocity modulating said intermixed beams of electrons and forming two sets of electron waves, means for extracting energy from said electron waves, and a collector electrode beyond said drift region in the direction of travel of said electrons for intercepting electrons passing through said enclosure.

6. The electron discharge device of claim 5 wherein said means for modulating and said means for extracting energy are resonant cavities.

7. The electron discharge device of claim 5 wherein said means for modulating is a helix.

8. The electron discharge device of claim 5 wherein said means for modulating is an input helix and said means for extracting energy is an output helix.

References Cited in the file of this patent UNITED STATES PATENTS 2,567,624 Thomson et al. Sept. 11, 1951 2,581,408 Hamilton Jan. 8, 1952 2,645,739 Fremlin et a1. July 14, 1953 2,760,097 Eber et al Aug. 21, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION atent Now 2,900,559 August 18, 1959 John A, Ruetz It is hereby certified that error appears in the above numbered patent .qui' ing correction and that the said Letters Patent should read as cort below:

In the drawings, Figure l, for the numeral l5 read l5 and for the numeral "3 read 3 same Figure l, the unlabeled reference numeral line extending to the first dotted grid should be labeled Signed and sealed this 5th day of April 1960.

(SEAL) Attest:

KARL AXLINE ROBERT c. WATSON Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,900,559 August 18, 1959 John A Ruetz t is herebycertified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below I In the drawings, Figure 'l, for the numeral "15'" read 15 and for the numeral "3 read 3 same Figure l, the unlabeled reference numeral line extending to the first dotted grid should be labeled "n I Signed and sealed this 5th day of April 1960 (SEAL) Attest:

KARL HQ AXLINE ROBERT c. WATSON Attesting Officer Commissioner of Patents 

